1. Field of the Invention
The present invention relates to equipment for extruding an expanded polymer sheet or plate, in particular polypropylene.
2. Description of Related Art
In the production field of expanded polymer products in the form of sheets or plates, in particular polypropylene, the equipment so far adopted does not allow an end-product to be obtained, with good resistance properties and at a low cost.
It should, in fact, be noted that polymers in general, and in particular polypropylene, have characteristics which do not allow easy expansion. Polypropylene in fact, in the molten state, at its characteristic Theological temperature, has a fluidity which is such that the action of gases, which tend to expand the cells, causes its structure to collapse.
It should also be considered that a polymeric material, such as polypropylene, is requested for its low cost and good mechanical and thermal resistance properties, and consequently, once expanded, has evident economic, ecological and technical advantages.
In this respect, methods are known which, by means of an extrusion process, allow this polymer to be chemically expanded with the sole use of particular chemical expanding agents. Chemical expanding agents however, whose use is necessary for this purpose with percentages equal to 2-6% with respect to the polymer, i.e. polypropylene, are of no economic advantage as they are considerably costly.
Furthermore, the use of physical gases is known, which are injected into the polymer, for example polypropylene, by means of injection processes, which do not allow an economically product to be obtained.
An objective of the present invention is to attempt to produce equipment for the extrusion of expanded polymers in sheets or plates, in particular expanded polypropylene, at reduced costs and with a high performance of the product obtained.
Another objective is to produce equipment for the extrusion of expanded polypropylene in sheets or plates, which is safe and ecologically valid, also in the presence of an expansion gas such as CO2.
These objectives according to the present invention are reached by the production of equipment for extruding an expanded polymer sheet or plate, in particular expanded propylene, as described in detail in claim 1.
Further characteristics are illustrated in the dependant claims.